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Fix a fixme: allow memdep to see past read-only calls when doing

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load dependence queries.  This allows GVN to eliminate a few more
instructions on 403.gcc:

 152598 gvn    - Number of instructions deleted
  49240 gvn    - Number of loads deleted
after:
 153986 gvn    - Number of instructions deleted
  50069 gvn    - Number of loads deleted



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60786 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-12-09 19:47:40 +00:00
parent 1559b3625b
commit 3579e44bf3
1 changed files with 13 additions and 4 deletions
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17
lib/Analysis/MemoryDependenceAnalysis.cpp
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@ -213,11 +213,20 @@ getPointerDependencyFrom(Value *MemPtr, uint64_t MemSize, bool isLoad,
// See if this instruction (e.g. a call or vaarg) mod/ref's the pointer.
// FIXME: If this is a load, we should ignore readonly calls!
if (AA->getModRefInfo(Inst, MemPtr, MemSize) == AliasAnalysis::NoModRef)
switch (AA->getModRefInfo(Inst, MemPtr, MemSize)) {
case AliasAnalysis::NoModRef:
// If the call has no effect on the queried pointer, just ignore it.
continue;
// Otherwise, there is a dependence.
return MemDepResult::getClobber(Inst);
case AliasAnalysis::Ref:
// If the call is known to never store to the pointer, and if this is a
// load query, we can safely ignore it (scan past it).
if (isLoad)
continue;
// FALL THROUGH.
default:
// Otherwise, there is a potential dependence. Return a clobber.
return MemDepResult::getClobber(Inst);
}
}
// No dependence found. If this is the entry block of the function, it is a